Anaesthetic gas scavenging systems are used to eliminate or at least minimise the potential harmful effects, both immediate and long term, of anaesthetic gases on doctors and staff in the operating theatre. Apart from the usual air conditioning in a theatre, it is also known to provide a device for connecting the outlet from the patient or anaesthetic machine as well as any pressure relief or "pop-off" valves in the anaesthetic circuit to an exhaust means. The exhaust means may be a ventilation system or a vacuum system, the latter being either part of the "building services" or a specially provided service. See, for example, CSA Standard CAN 3-Z 168.8-M, Anaesthetic Gas Scavenging Systems, prepared and published by the Canadian Standards Association.
This invention is concerned with devices for use with vacuum systems. An example of such a device is disclosed in U.S. Pat. No. 4,291,689 W. W. Hay. The device comprises housing means forming a fluid path between an inlet port and an outlet port; a variable restriction means in the housing and forming a restriction of the fluid path; chamber means in the housing between the restriction means and one of the ports; and pressure relief valve means for venting the chamber means when a predetermined pressure limit is exceeded. Hereinafter a device of this type is referred to as "a device of the type set forth".
The restriction means of U.S. Pat. No. 4,291,689 is a needle valve settable by an operator, usually the anaesthetist, to establish a desired flow of gas to the vacuum system.
Experience by the inventor of several devices of this kind in an anaesthetic gas scavenging system has revealed several problem areas. A major problem is fluctuations of flow rate and pressure in the inlet chamber as the supply rate, ie from patient and anaesthetic gas supply, and vacuum pressure vary. With a building service vacuum supply the latter is practically unavoidable owing to the demands placed on the system by other users. Another major problem is the contamination of the device by the heavy components of the anaesthetic gases, such as Halothane and Penthrane. These components cause build up of tar which on the one hand blocks the needle valve and relief valves and on the other hand aggressively attacks the rubber and plastics elements and seals.
This invention seeks to overcome or at least ameloriate the above mentioned problems in a satisfactory, inexpensive manner.